AN ADJUSTABLE-SPEED GEAR DEVICE FOR AN ENERGY-GENERATING PLANT

Abstract

A variable-speed transmission for a power-generating plant; with an input shaft which is connected at least indirectly with a power transducer of a wind-energy generator or hydro-electric generator; with an output shaft which is connected at least indirectly with an electric generator, with the speed of the output shaft being substantially constant; with a superposition gear which is connected at least indirectly with the input shaft and which divides power among a first power branch connected at least indirectly with the output shaft and a second power branch; with the second power branch comprising at least two hydrodynamic circulations, with at least one of the hydrodynamic circulations being at least indirectly in connection with the first power branch.

Full Text

A vanable-speed transmission for a povaer-generating plant
Tl e invention relates to a variable-speed transmission for a power-generating
p'ant, especially such a one which is driven by a fluid flow engine such as a wind-
e lergy generator or hydro-electric generator and produces electric power by
r leans of an electric generator.
^ower-generating plants which remove kinetic energy from an air or water flow by
Tieans of a power transducer show special characteristics for two reasons. On the
one hand, the maximum available kinetic energy of the flow medium fluctuates
over time. On the other hand, the power conversion of the kinetic energy of the
flow into the kinetic energy of the power transducer (e.g. a wind rotor or a water
turbine) shows inherent characteristics which assign to each flow speed an optimal
speed of the power transducer in which a maximum power conversion occurs. The
assigned flow speeds and the optimal speeds depend on the geometrical
configuration of the power transducer. The associated flow speeds and the optimal
rotational speeds depend on the dimensions and the geometrical configuration of
the power transducer, ft follows from this that the power-generating plant such as
a water or hydro electric plant must preferably be operated with a VBriable input
speed which on its part must be adjusted as optimal as possible to the respectively
appfed flow speed of the working medium.
A further requirement placed on a power-generating plant as described above is
obtained from the fact that the electric generator is connected to an interconnected
network -grid which typically works with a constant system frequency. Since the
constant system frequency concerns the primary control variable for stabilizing an
interconnected network grid, the power supplied by the power-generating plant
into the grid must be supplied in a frequency~and phase-conform manner. On the
one hand, this can be achieved by a frequency converter which allows exciting a
generator with the respectively required frequency to compensate the difference to
the system frequency and to thus realize a variable-speed generator. The difficulty
in this approach for power-generating plants driven by the kinetic energy of a flow

r ledium is that the power absorption characteristics of a wind rotor or a water
t irbine can be emulated only within limits for a frequency converter and complex
r jquirements are placed on the open-loop or closed-loop control as a result of the
s:iffness of the defined generator characteristics by the frequency converter. As a
pasult, the known realizations where frequency converters are realized for linking a
conventional power-generating plant to an interconnected grid network are not
cotimal for the reason that harmonic loads on the grid and the generation of
s gnificant reactive power are unavoidable. A contrary path is therefore described
if the present application and a variable-speed transmission is proposed for a
conventional power-generating plant whose output shaft revolves substantially
v\ ith a constant speed and an input speed can be realized which is speed-variable
a the same time and can be guided along an optimal setpoint speed. This enables
both driving a speed-constant electric generator as well as realizing optimal power
aosorption from the flow medium in the part-load range.
T ie following approaches have become known for the transmission that meets
these requirements:
Ir a first system, the kinetic energy taken up by the power transducer from the flow
rr edium is transmitted to a superposition gear. A power division to an electric
g( ;nerator and a small servo-motor is realized in the superposition gear.
Aijproximately one-third of the input power is usually transmitted to the
servomotor. As a result of the fact that the servomotor is operated with different
frequencies either as a motor or as a generator, the generator speed can be
St abilized and that the generator can be operated in a frequency-locked manner
ai d can be connected directly with the grid. The servomotor on its part is
connected by a frequency converter to the grid or is supplied alternatively by an
ai xiliary motor which is coupled mechanically with the generator. The described
s> stem is complex with respect to its control technology and is limited in its
efficiency. The problems as explained above also occur when using frequency
cc nverters.

I ne electric servomotor is replaced in a second system which operates hydro-
s atically by hydraulic pumps and motors. The problem of complex control
c naracteristics also occur in this case. An additional factor is a sluggish response
c naracteristic and relevant delay times and high non-linearity factors as a result of
t ie hydraulic components.
II power-generating plants such as wind and water power stations, there are
1 jrther requirements in addition to the principal problems as described above in
• ;onnection with the drive of an electric generator which is coupled with an
nterconnected grid network. These arise from special operating states such as the
jtarting or stopping process, the load shedding as a result of a serious grid
nstabiiity or speed limitation on the input shaft under full load conditions. The latter
equirement is obtained especially in wind power stations whose rotor blade tips
should not exceed a certain speed in order to keep the noise below a certain
[hreshold value. The respective threshold value can vary depending on the
location of the wind power station such as an onshore or offshore location. Even in
the case of the speed-limited wind power station, there should remain a certain
softness in the reactivity, which means that under the occurrence of a wind gust
even a speed-limited wind power station should allow an increase of the rotor
speed for a short period which is then returned to the threshold value immediately
thereafter. If the transmission meets such a requirement, any occurring power
impulses can be limited. It is preferable vi/hen the additional energy made available
by a wind gust is taken up by the power-generating plant and can be utilized in the
form of higher power output.
The invention is based on the object of providing a power-generating plant which
comprises a transmission which meets the above requirements. Especially, the
transmission should produce a substantially constant output speed for driving an
electric generator coupled directly with an interconnected grid network. The input
shaft should follow in a speed-variable manner the optimal power absorption
characteristics for the power transducer such as the wind rotor or the water
turbine. Moreover, the input speed should also be guidable or reducible above a

predetermined threshold value. In addition to speed limitation, such operating
: tates are starting or stopping phases or load shedding for example. A
1 'ansmission for a power-generating plant is further provided which shows a
lavorable control characteristic and a certain softness in the reactivity and is
characterized by simplicity in construction and production.
n order to achieve this object, the inventors have recognized that the power flow
1 the transmission needs to be divided into at least two power branches with at
east two hydraulic circulations. For this purpose, the transmission comprises in a
)referred emibodiment a superposition gear which is at least indirectly in operative
;onnection with the input shaft and divides the power flow among a first and
second power branch. The first power branch is connected at least indirectly with
he output shaft which drives the electric generator. The demanded constancy of
he frequency of the output shaft is achieved by the open-loop or closed-loop
control of the power flow in the second power branch.
n accordance with the invention, the second power branch comprises at least two
lydrodynamic circulations, with at least one of the hydrodynamic circulations
producing an operative connection between the first power branch and the second
jower branch on the driven side to the superposition gear. Notice must be taken
hat the power flow in the second power branch can be directed both forwards or
oackwards. The forwards direction shall be understood in such a way that the
Dower flow occurs in the driven direction. In this case, the power introduction is set
Tom the second to the first power branch by means of the hydrodynamic
circulation connecting the first and the second power branch. If the power is
guided back to the second power branch instead, meaning that it flows back from
:he first power branch to the superposition gear, there is consequently a reactive
Dower flow which can also be regulated in such a way that the mentioned
requirements placed on the transmission of the power-generating plant are
fulfilled.

In addition to the first hydrodynamic circulation, the second power branch
cj^mprises at least one second hydrodynan^iic circulation. The additional
c )nstructional effort required for the second hydrodynamic circulation is offset by a
Isrge number of advantages. On the one hand, the second hydrodynamic
c rculation can have a different design or a different configuration in comparison
with the first hydrodynamic circulation.
.Suitable hydrodynamic circulations are hydrodynamic converters, hydrodynamic
couplings, retarders and TRILOK torque converters. Each one of these
lydrodynamic circulations offers benefits for certain applications or operating
areas. If a hydrodynamic converter is used for coupling the first and second power
oranch, then this leads to the special advantage that the characteristics of the
nydrodynamiic converter correspond to the characteristics of a power transducer
driven by a natural resource such as a wind rotor or a water turbine and for this
reason the required constancy of the frequency of the driven shaft is obtained
automatically as a result of self-regulation characteristics, which will be explained
below in closer detail.
Although it is not possible to realize any self-regulation characteristics for a
hydrodynamic coupling, there are still advantages for a hydrodynamic coupling in
comparison with a hydrodynamic converter due to the high efficiency in certain
operating areas. This applies especially to the full-load area where the input speed
of the transmission is guided and is limited in most cases. The TRILOK torque
converter on the other hand combines advantages in certain operating areas with
respect to efficiency and control characteristics. As a result, different
hydrodynamic circulations each offer advantages for certain operating areas or
operating states, so that different types of hydrodynamic circulations can be
combined when using at least two hydrodynamic circulations. Depending on the
requirements, it is then possible to switch between the hydrodynamic circulations
or to change the respective weighting. This can be fulfilled in the easiest way by
setting the filling level with working medium in the hydrodynamic circulations.

In addition to tiie use of different designs of liydrodynamic circulations, it is also
possible to use several similar types such as two hydrodynanriic converters which
are arranged parallel in the second power branch. They differ by their design
characteristics or as a result of transmission components assigned upstream or
downstream. It is thus possible to adjust the transmission in accordance with the
invention to different operating states. If different designs are available, it is also
possible by changing the design to adjust in an improved manner to the time-
changeable power potential of the natural resource.
An advantageous embodiment of the invention further provides that the second
hydrodynamic circulation is used for the open-loop and closed-loop control of a
first hydrodynamic circulation. The first hydrodynamic circulation usually assumes
the task of regulating or controlling the power flow from the first power branch to
the second power branch and vice-versa. This is usually achieved by a reaction
member. These are the guide blades for a hydrodynamic circulation for example. If
the requirement arises from a certain operating state that the self-regulation
characteristic and the thus linked optimal setting of the guide blades is left, then it
is necessary to change the originally optimal setting of the guide blades. This
leads to flow losses in the hydrodynamic converter and a reduced efficiency in this
connection. Moreover, a mechanical adjusting mechanism which is necessary for
this purpose is not free from wear and tear, which plays a role in the respect that
for all operating states outside of the self-regulation characteristic it is necessary to
react to the fluctuating power input from the natural resource by providing a
permanent change in the guide blade setting. In addition to the frequency of the
setting of the guide blade position, it is also necessary to take note in this case of
the usually high requirements placed on the reaction speed. With the second
hydrodynamic circulation (e.g. a retarder), the necessary adjustment is not
achieved by an adjusting movement of the action member, which in the case of a
hydrodynamic converter are the guide blades, but rather by a weighting between
the first and the second hydrodynamic circulation in the second power branch. If a
change in the weighting on the other hand is produced by setting the respective

filling level with working mediunn, such a change can be performed virtually without
wear and tear and can be repeated as often as desired.
The invention is now explained in closer detail by reference to the enclosed
drawings, wherein:
Fig. 1 shows a variable-speed transmission with a first and second power
branch, with the second power branch comprising a hydrodynamic
converter and a hydrodynamic coupling.
Fig. 2 shows the power/speed characteristics for a transmission according
to Fig. 1.
Fig. 3 shows a variable-speed transmission with a first and second power
branch, with the second power branch comprising two hydrodynamic
converters.
Fig. 4 shows the power/speed characteristics for a transmission according
to Fig. 3.
Fig. 5 shows a variable-speed transmission with a first and second power
branch, with the second power branch comprising a hydrodynamic
converter and a retarder.
Fig. 6 shows the power/speed characteristics for a transmission according
to Fig. 5.
Fig. 7 schematically shows the active-power curve at the best point of a
wind power station.
The rotor power Pr of a wind power station is in connection by approximation with
the wind speed Vw:

T ie expression k combines various constant values such as the blade geometry
aid the density of the air. Cp further designates the power conversion coefficient,
v/hich on its part depends on the wind speed Vw, the rotor speed lor and the
inguiar position of the rotor blades, the so-called pitch angle p. This power
;onversion coefTicient is characterized by a global maximum which shifts towards
ligher rotor speeds ojr under rising wind speeds v^.
Fig. 7 shows this connection by showing the real power of a wind rotor by taking
various wind speeds into account. The figure shows a group of curves {continuous
curves), which by way of example show the power taken up by a wind rotor with a
diameter of 70 m from the air flow at constant rotor blade position for the wind
speeds of 18 m/s, 16 m/s, 14 m/s, 12 m/s, 10 m/s, 8 m/s for various rotor speeds.
The displacement of the optimal rotor speed towards higher values with rising wind
speed is characteristic. The respective power maximums are situated on a curve
which is also known as paraboUcs. Guiding the speed along this cuwe of optimal
power absorption is designated below as power-optimal speed guidance for the
input shaft of the transmission in accordance with the invention. A variable-speed
system can thus be operated at optimal power conversion coefficients depending
on the available wind speed. In addition to variable-speed operation at partial load,
wind power stations are typically configured for certain nominal power in
conjunction with a nominal speed which are each reached and held at full load.
Fig. 7 shows the torque of the wind rotor for the above wind speeds for different
rotor speeds on the basis of the group of curves shown with the broken lines. The
illustrated torque cun/es are associated with the powers that depend on the wind
speed, i.e. there is a torque value which belongs to each power-optima! speed,
which does not correspond to the maximum torque at the respective wind speed
but assumes another value (see in this connection the bold torque progress curve
in Fig. 7). The electric generator is driven with this torque taken up by the wind

otor via the transmission in accordance with the invention. The torque/speed ratio
or a synchronous generator as shown in Fig. 7 proves that for an impressed
system frequency of 50 Hz on the driven shaft of the transmission a constant
speed of 15(D0 rpm (for this example) is predetermined on the driven side for the
different transmitted torques, if an asynchronous generator is used instead of the
synchronous generator, the situation can be seen accordingly, because in
operation in the linear region it is possible to assume such a steep torque/speed
ratio that the speed of the driven shaft of the transmission has a substantially
constant value.
Fig. 1 shows a first embodiment of a transmission 1 in accordance with the
invention. It comprises a first power branch 7 and a second power branch 18, with
two hydrodynamic circulations, a hydrodynamic converter 12 and a hydrodynamic
coupling being arranged in parallel in the second power branch. Both are in an at
least indirect operative connection with the first power branch 7. The illustration
shows a transmission 1 in detail whose input shaft 2 is connected at least
indirectly with a wind power station. In the present case, a first transmission 4 is
positioned with a constant transmission ratio between the rotor 3 of the wind
power station and the input shaft 2. In the embodiment as shown here, a
superposition gear 5 for branching the power in transmission 1 (for example a
planetary gear) is used, with the input shaft 2 being in connection with the planet
carrier 6 and driving the same with speed n1.
On the driven side to the superposition gear 5 there are now two power branches.
The first power branch 7 guides power via the sun wheel 9 to the output shaft 10
of the transmission 1. This output shaft 10 which revolves with a constant speed
drives the electric generator 11 at least indirectly and is in operative connection
with the hydrodynamic converter 12. For this purpose, the output shaft 10 is
connected at least indirectly with the pump wheel 13 of the hydrodynamic
converter 12. A guide wheel with adjusting blades is used as a reaction member
15 in the hydrodynamic converter 12, with which the power flow to the turbine

V heel 14 can be set. The reaction member is arrested at an optimized position in
t le present embodiment during the operation of the transmission 1.
" he turbine v/heel 14 of the converter 12 is in an at least indirect connection with a
f jrther gear component in the second power branch 18 (e.g. a second
! uperposition gear 22) which is used for the combination of the partial power flows
lor the two hydrodynamic circulations. Each of the hydrodynamic circulations is
jssociated with a partial power flow. A first partial power flow 18.1 occurs by the
lydrodynamic converter 12 and a second partial power flow 18.2 by the other
lydrodynamic coupling 30. For this purpose, the pump wheel 31 of the
lydrodynamic coupling 30 is in an at least indirect operative connection with the
irst power branch 7 and transmits, depending on the filling level with working
Tiedium in the hydrodynamic coupling 30, a torque or a power flow via the turbine
awheel 32 and an interposed gear component such as a stationary transmission
16.2 to the further transmission components 16.2 and the second superposition
gear 22.
The relative ratio between the first partial power flow 18.1 and the second partial
power flow 18.2 can be set by the filling levels with working medium in the
hydrodynamic converter 12 and the hydrodynamic coupling 30. When there is a
partial load condition on the energy-absorbing wind rotor 3, it is preferable to
activate merely the hydrodynamic converter. The same comprises a respectively
optimized, but fixed position of the reaction member 15. In the transition to full load
there is a change to the hydrodynamic coupling, which allows reducing the rotor
speed of the wind power station.
Figure 2 shows the different operating ranges for a transmission according to Fig.
1 where either the hydrodynamic converter 12 or the hydrodynamic coupling 30
are activated. The illustration shows the mechanical output of the transmission 1
depending on the input speed. A first transmission was omitted for reasons of
simplification, so that the input speed corresponds to the rotor speed in the case of
a wind power station. The output is stated in random units because the respective

absolute values depend on the individual size and geometry of the power
transducer of the power-generating plant. The transmission is operated in the
converter range in the present embodiment for input numbers below 16.3 rpm. A
group of cur^/es 201, 202, 203, 204 and 205 are shown. Each curve corresponds
to a different setting of the reaction member 15 of the hydrodynamic converter 12.
The transmission ratio in the superposition gear 5 and optionally the further gear
components which may be provided upstream or downstream to the converter is
chosen within the scope of the expertise of the person skilled in the art. Similarly,
the dimensioning of the converter is adjusted, so that the power absorption
characteristics of the rotor 3 of the wind power station is emulated substantially by
the converter for an optimal position of the reaction member and that thus a
constant speed can be achieved on the output shaft 10 within the terms of self-
regulation characteristics. The wind rotor can thus be operated with the power-
optimized speed along the parabolics. This optimal position of the reaction
member 15 substantially corresponds to the one with the reference numeral 204.
The electric power of the generator in the converter region will follow this
characteristic accordingly, which is shown in Fig. 2 with a broken line 250 for the
rotor speeds
invention translates the typically low input speed into a high output speed which
drives the generator. The hydrodynamic circulations which are arranged on the
driven side to the superposition gear 5 for power branching in the second power
branch can be operated with a high rotational speed and thus efficiently.
In the present embodiment, it is necessary to provide a speed limitation of the
wind rotor for higher power inputs. The reasons for this can be the noise
development or aspects concerning the strength of individual components. For this
purpose, a changeover is made to the hydrodynamic coupling 30 preferably above
a certain speed threshold and the output follows the curve 210 which is associated
with the hydrodynamic coupling. The precise position and the steepness of the
characteristic curve can be configured by the dimensioning of the hydrodynamic
coupling 30 and the gear components associated with the same upstream or

downstream within the discretion of the person skilled in the art. In a further
development, the transition between the converter region and the coupling region
:an be switched in a graduated manner by partly filling or emptying the respective
lydrodynamic circulations.
n the coupling region, there is preferably such a steep characteristic curve of the
lydrodynamic coupling 210, so that a limitation of the rotor speed is achieved
vithin a wide margin.
A changeover from the converter region to the coupling region is preferably also
i nade for the above described transmission 1 in accordance with the invention
when the hydrodynamic coupling 30 has a higher efficiency relative to the
t lydrodynamic converter 12. Power losses in the transmission can thus be
minimized.
; Jince the hydrodynamic coupling 30 needs to be configured in a controllable
nanner anyv/ay, it is preferred to run through with the hydrodynamic coupling 34
1 jrther special operational situations such as the starting or the breaking of the
[ ower-generating plant. Such a preferred application of the high dynamic coupling
i; also given in the case of load shedding. The changeover between the different
\ ydrodynamic circulations can be achieved by setting the filling level with the
v/orking medium in the hydrodynamic converter 12 or the hydrodynamic coupling
: 0.
/, further preferred embodiment of the second power branch 18 of the
transmission is shown in Fig. 3. The connection between the first power branch 7
and the second part branch 18 is produced by two hydrodynamic circulations of
t le same type, the first hydrodynamic converter 12 and a second hydrodynamic
c Dnverter 24.
1 he parallel partial power flows 18.1 and 18.2 in the second power branch 18
V hich start out from the first hydrodynamic converter 12 and the second

hydrodynannic converter 24 are combined by a further gear component (e.g. a
second superposition gear 22) and guided back via the internal geared wheel 17
to the superposition gear 5. Both the first as well as the second hydrodynamic
converter each access the first power branch 7 at least indirectly via their pump
wheels 13, 25 and are each at least in indirect operative connection with the
second power branch 18 via the turbine wheels 14 and 27. The guide wheels 15
and 28 are shown as being set in a fixed manner in the present case.
By using two hydrodynamic converters 12, 24 in parallel pick-off from the first
power branch 7 it is possible to switch between two different configurations of the
transmission 1. The differences in design can be produced by the constructional
adjustment of the first and second hydrodynamic converter 12 and 24 and by
interposing additional gears in the partial branches. This is shown in Fig. 2 on the
basis of stationary transmission 16.1 which is integrated in the partial branch
starting from the first hydrodynamic converter 12 for the first partial power flow
18.1. By using two hydrodynamic converters it is possible to extend the self-
egulation characteristics of the transmission over a wide range of power input. It
s also possible to configure the second hydrodynamic converter and possible
downstream gear components in the second power branch in such a way that the
second partial branch for the second partial power flow 18.2 is used for the
ransition to the full-load region, such that rotor speed is guided along a setpoint
;urve in addition to the speed of the output shaft which is kept substantially
constant.
The ratio of the partial power flows through the first hydrodynamic converter 12
ind the second hydrodynamic converter 24 can be achieved in a wear-free
nanner through a respective setting of the filling level with working medium. It is
ilso possible to operate each hydrodynamic converter on its own. A parallel
)peration and the individual setting of the speed/torque ratio for each
jydrodynamic converter are possible. Moreover, a changeover is made according
0 a preferred embodiment of the invention between the two hydrodynamic
> ;onverters 12, 23, which means that they are not operated simultaneously with the

exception of one changeover range which is limited to a narrow speed interval. As
a result, the entire power flow on the second power branch 18 outside of the
changeover region is associated either to the first partial power flow 18.1 or the
second partial power flow 18.2.
Fig. 4 shows the family of characteristics 42 differently configured hydrodynamic
converters 12 and 24 for a transmission in accordance with the invention
according to Fig. 3. According to Fig. 2, the output of the transmission 1 is entered
in random units against the input speed. A family of characteristics with broken
lines is shown for the first hydrodynamic converter 12 the different settings of the
reaction member 301, 302, 303, 304 and 305. The self-regulation characteristics
are linked to an optimal setting of the reaction member which substantially remains
the same. In the present illustrated case, this corresponds substantially to the
setting with the reference numeral 304. The second hydrodynamic converter is
configured for higher input speeds and shows a steeper family of characteristics.
This is possible within the scope of the expertise of the person skilled in the art by
respective dimensioning of the second hydrodynamic converter 24 and by
providing upstream or downstream gear components. In Fig. 3, a stationary
transmission 16.1 is associated on the turbine side to the first hydrodynamic
converter for example, whereas this was omitted for the second hydrodynamic
::onverter 24.
n Fig. 4, the family of characteristics assigned to the second hydrodynamic
converter 24 is outlined by the group of curves 401, 402, 403, 404 and 405, with
each of these curves corresponding to a different position of the reaction member
28 of the second hydrodynamic converter 24. In accordance with this, the group of
curves 301, ^|, 303, 304 and 305 outline the input speed/output characteristics
Df the transmission when filling the first hydrodynamic converter 12, each for
different position of the reaction member 15.
t is now possible to change over between the two groups of characteristics by
naking a respective setting of the respective filling level with the working medium

f 3r the two hydrodynamic converters 12, 24. This occurs in Fig. 4 above a rotor
! peed of 15 rpm, so that the resulting ratio of the input speed and output for the
t imbodiment of a transmission in accordance with the invention as shown here is
designated v/ith the reference numeral 350, with an optimal setting of the reaction
nember being chosen for both converters.
-ig. 5 shows a further embodiment of a variable-speed transmission in accordance
^ith the invention with a power branch between a first power branch 7 and a
second power branch 18 by means of a superposition gear 5, with the second
power branch 18 comprising two hydrodynamic circulations arranged in parallel. In
the present case these are a hydrodynamic converter 12 and the retarder 20. The
further components correspond to the drive trains according to figures 1 and 3 and
are designated with corresponding reference numerals.
As a modification to the embodiments as described above, the embodiment
according to figure 5 only comprises a connection on the driven side of the first
power branch 7 and of the second power branch 18 via a hydrodynamic converter
12. Although the second hydrodynamic circulation in the second power branch 18
(retarder 20) also acts back at least indirectly to the superposition gear 5, it does
not link the first power branch 7 with the second power branch 18.
Fig. 6 on the other hand shows that the retarder is used for leaving the region of
power-optimal guidance in the transition to full load without requiring any
adjustment in the first hydrodynamiic circulation, namely the hydrodynamic
converter 12. It is operated with a constant setting of the reaction member 15, i.e.
with a constant setting of the guide blades. Figure 6 again shows in detail the input
speed entered against the output in random units. Below a speed threshold, which
in the present case is slightly above 16 rpm, only the hydrodynamic converted 12
is filled and operated with a fixed position of the guide wheel where the wind rotor
revolves in a power-optimal manner. In the present example it substantially
corresponds to the setting of the reaction member which is designated with the
reference numeral 504. The further cur\/es 501, 502, 503 and 505 of the group of

( haracteristics are assigned to further positions of the reaction member which are
I ot optimal for the present case. The retarder 20 is filled above the mentioned
I peed threshold, to which retarder there is assigned a retarder characteristic 600.
I: is substantially steeper than the chosen converter characteristics, so that
; ubstantially there is a limitation in the rotor speed. The thus resulting electric
I lower output of the generator depending on the rotor speed is shown in figure 6
' vith the curve 550 which is shown in a broken line.
'he advantage of a transmission in accordance with the invention according to
igure 5 as compared with a variant where the second hydrodynamic circulation
which in this case is the retarder 20) is that in the event that the operating state of
)Ower-optimal guidance of the wind power station needs to be left (e.g. because a
imitation in the rotor speed becomes necessary under full load conditions for
example) there is no mandatory change in the guide wheel position. Without the
second hydrodynamic circulation it would then generally not be possible to work
vith a substantially constant guide wheel position over a wide power range of the
latural resource. Instead, the power flow via the hydrodynamic converter 12 would
lave to be controlled actively via a time-variable setting of the guide wheel. In
addition to the high requirements placed on the mechanical wear and tear and the
eactivity, it is disadvantageous in such case that the hydrodynamic converter 12
;an no longer be operated with the highest possible efficiency. According to figure
3, an additional hydrodynamic circulation (which in this case is a retarder 20) is
ntegrated in the second power branch 18 parallel to the hydrodynamic converter
12. In order to avoid an adjustment of the guide wheel 15 of the hydrodynamic
converter 12 for special operating states outside of the power-optimal operating
state of the self-regulation, the filling level in retarder 20 is adjusted in such a way
that the power flow is controllable on the second power branch 18 without
changing the setting of the hydrodynamic converter 12. Moreover, it is also
possible to change over completely from the hydrodynamic converter 12 to the
retarder 30 iin accordance with the explanations above. In such a transition from
the converter to the retarder region, the connection between the first power branch
Claims:
A variable-speed transmission for a power-generating plant;
1 with an input shaft (2) which is connected at least indirectly with a power
transducer of a wind-energy generator or hydro-electric generator;
2 with an output shaft (10) which is connected at least indirectly with an
electric generator (11), with the speed of the output shaft (2) being
substantially constant;
.3 with a superposition gear (5) which is connected at least indirectly with the
input shaft (2) and which divides power among a first power branch (7)
connected at least indirectly with the output shaft (10) and a second power
branch (18);
.4 with the second power branch (18) comprising at least two hydrodynamic
circulations, with at least one of the hydrodynamic circulations being at least
indirectly in connection with the first power branch (7).
A variable-speed transmission for a power-generating plant according to
claim 1, characterized in that a hydrodynamic converter and/or a
hydrodynamic coupling and/or a TRILOK torque converter and/or a retarder
are used as hydrodynamic circulations in the second power branch (18).
A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 2, characterized in that the hydrodynamic
circulations are arranged in the second power branch (18) in parallel.
A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 3, characterized in that means are provided to
change the filling level of the working medium in the individual
hydrodynamic circulations of the second power branch (18).

5. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 4, characterized in that a hydrodynamic
converter which is used as one of the hydrodynamic circulations in the
second power branch (18) is operated with a fixed guide wheel position.
6. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 5, characterized in that the output shaft (10) has
a higher speed than the input shaft (2).
7. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 6, characterized in that the second power
branch (18) comprises at least one stationary transmission (16).
8. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 1, characterized in that the connection between
the first power branch (7) and the second power branch (18) is produced by
means of a hydrodynamic converter (12), with the pump wheel (13) of the
hydrodynamic converter (12) being connected at least indirectly with the
first power branch (7) and the turbine wheel (14) of the hydrodynamic
converter (12) at least indirectly with the second power branch (18).
9. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 7, characterized in that the connection between
the first power branch (7) and the second power branch (18) is produced by
means of a hydrodynamic coupling (30), with the pump wheel (31) of the
hydrodynamic coupling (30) being connected at least indirectly with the first
power branch (7) and the turbine wheel (32) of the hydrodynamic coupling
(30) at least indirectly with the second power branch (18).
10. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 7, characterized in that the connection between
the first power branch and the second power branch is produced by means

of a TRILOK torque converter, with the pump wheel of the TRILOK torque
converter being connected at least indirectly with the first power branch (7)
and the turbine wheel of the TRILOK torque converter at least indirectly with
the second power branch (18).
1. A variable-speed transmission for a power-generating plant according to at
least one of the claims 9 to 10, characterized in that a retarder (20) is
connected at least indirectly with the second power branch (18).
12. A variable-speed transmission for a power-generating plant according to at
least one of the claims 1 to 11, characterized in that a first hydrodynamic
circulation produces a first connection between the first power branch (7)
and the second power branch (18) and a second hydrodynamic circulation
produces a second connection betiween the first power branch (7) and the
second power branch (18), with the power flows from the first hydrodynamic
circulation and from the second hydrodynamic circulation being combined in
the first power branch (7) by means of a second superposition gear (22).
13. A variable-speed transmission for a power-generating plant according to
claim 12, characterized in that the first hydrodynamic circulation is a
hydrodynamic converter (12) and the second hydrodynamic circulation is a
hydrodynamic coupling (30).
14. A variable-speed transmission for a power-generating plant according to
claim 13, characterized in that a stationary transmission (16.2) is interposed
between the hydrodynamic coupling (30) and the second superposition
gear (22).
15. A variable-speed transmission for a power-generating plant according to
claim 14, characterized in that the first and second hydrodynamic circulation
are hydrodynamic converters.

16. A variable-speed transmission for a power-generating plant according to
claim 15, characterized in that a stationary transmission is interposed
between at least one of the turbine wheels of the hydrodynamic converters
and the second superposition gear (22).
17 A pov/er-generating plant, comprising:
17.1 a power transducer of a wind-energy or hydro-electric generator;
17.2 an electric generator;
17.3 a variable-speed transmission according to at least one of the claims
1 to 16.
18. A method for the open-loop and/or closed-loop control of a transmission (1)
or a power-generating plant according to at least one of the claims 1 to 17,
characterized in that the filling of the hydrodynamic circulations in the
second power branch (18) of the transmission (1) is made depending on the
input speed of the transmission.
19. A method for the open-loop and/or closed-loop control of a transmission (1)
or a power-generating plant according to claim 18, characterized in that in
the second power branch (18) of the transmission a first hydrodynamic
circulation is filled with working medium and a second hydrodynamic
circulation is emptied below a first speed threshold for the input speed, and
the first hydrodynamic circulation is emptied and the second hydrodynamic
circulation is filled with working medium above a second speed threshold for
the input speed.

A variable-speed transmission for a power-generating plant;
with an input shaft which is connected at least indirectly with a power
transducer of a wind-energy generator or hydro-electric generator;
with an output shaft which is connected at least indirectly with an electric
generator, with the speed of the output shaft being substantially constant;
with a superposition gear which is connected at least indirectly with the input
shaft and which divides power among a first power branch connected at least
indirectly with the output shaft and a second power branch;
with the second power branch comprising at least two hydrodynamic
circulations, with at least one of the hydrodynamic circulations being at least
indirectly in connection with the first power branch.